The field of the Invention is computer-controlled three-dimensional (“3D”) object formation via deposition of materials to create objects. Most viable means of 3D object formation are effected via computer aided design, employing a machine and materials developed for this purpose.
Generally called “Three-dimensional printing,” and “3D Printing,” this process has also been referred to as “Stereolithography,” “Rapid Prototyping,” and “Additive Manufacturing,” among other names, usually depending upon the chosen method.
3D object building can be generally defined as the serial, layer-wise deposition and stacking of sequential cross-sections of an object. The methods available are varied and include sintered powder layers affixed by lasers or sprayed adhesive, ink jet droplets of monomers UV/photo-curing in situ, extruded plastic filament heated to melting, deposited and then cooled to reform as a solid, and more. In addition to the additive methods, subtractive methods are employed, referring to the computer-controlled removal of material for shaping of layers. All the aforementioned are included the field of this invention. Following this introduction is a further discussion and list of methods and comparisons between them.
Three-dimensional “3D” Printing, also known as “Additive Manufacturing,” is a relatively new field of science wherein objects are built via Computer Aided Modeling, triggering the controlled layer-wise deposition of curable or harden-able/catalyzed materials using various processes, to build a three-dimensional object.
In general, additive processes are used, wherein successive layers of build material are deposited and stacked according to the requisite geometry of each cross-section layer of the object being built. These objects can be of almost any shape or geometry, and are produced from a 3D model or other electronic data source. The building occurs wherein a tracing of x/y planes is effected via mechanical movement similar to that of a print head over paper in a printer. Instead of depositing ink, the head is depositing an adhesive, a thermoplastic, or other buildable material; or the tracing mechanism may be delivering a catalyst such as curative laser beam scanning through a pool of photopolymer liquid. Instead of feeding sequential pages as in a two-dimensional printer, the build area, or the area where commonly a stack of paper would be found, would move downwards on a z-axis (vertically) to accommodate the next subsequent layer, or instead the print head holding-mechanism will move upwards on the z-axis after the completion a subsequent layer, atop the previous one, after it has been completed.
There is a plurality of processes that sequentially deposit material. Moreover, recently the meaning of the term has expanded to encompass a wider variety of techniques, such as ink jet-, extrusion-, and sintering-based processes. Generally, the terms “Additive Manufacturing” and “3D Printing” are interchangeable parlance for any method of 3D object creation, generally via computer aided design. In addition, it is commonly called, “Rapid Prototyping” (RP).
Early Additive Manufacturing, (abbreviated as “AM”), equipment and materials were first developed in the 1980's. For example in 1981, Hideo Kodama of Nagoya Municipal Industrial Research Institute invented two AM fabrication methods of a three-dimensional plastic model with photo-hardening polymer, wherein the UV-exposure area is controlled by a mask pattern, or the scanning fiber transmitter.
Then in 1984, Charles Hull of 3D Systems Corporation developed a prototype system based on this process known as “Stereolithography,” in which layers are added by curing photopolymers with ultraviolet light lasers. Hull defined the process as a, “system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed,” but this had been already invented by Kodama. Hull's important contribution to 3D printing is the design of the STL (STereoLithography) 3D printing software file format widely accepted by most users, as well as the digital slicing and infill strategies common to many processes today.
The term “3D Printing” originally referred to a process employing customized inkjet print heads to deliver materials for building objects.
The technology used by most 3D printers to date—especially hobbyist and consumer-oriented models—is fused deposition modeling (FDM), a specialized micro-application of thermoplastic extrusion.
Any AM process for metal sintering or melting, (such as selective laser sintering, direct metal laser sintering, and selective laser melting), was generally referred to by its specific nomenclature in the 1980's and 1990's. Nearly all metalworking production at the time was by casting, fabrication, stamping, and machining; even though automation was frequently applied to those technologies, (such as by robot welding and CNC), the idea of a tool or head moving through a 3D work-envelope transforming a mass of raw material into a desired shape layer by layer, was associated by most people only with processes that removed metal, (Subtractive), rather than adding it, such as CNC milling, CNC EDM, and others.
By the mid-1990's, new techniques for serial layer-wise material deposition were developed at Stanford University and Carnegie Mellon University, including Micro-casting and sprayed materials.
Sacrificial parts, sprues, and support materials had also become more common, enabling the printing of new object geometries with negative space or delicate freestanding parts. Additive AM-type sintering was beginning to take hold as a viable means of metal object creation.
The umbrella term “Additive Manufacturing” gained wider exposure in the decade of the 2000's, as the various additive processes began to mature. With regard to metal, it became clear that soon metal removal would no longer be the only metalworking process done under that type of control. It was during this decade that the term “Subtractive Manufacturing” appeared as a retronym for the large family of machining processes with metal removal as their common theme.
During that time, the term “3D Printing” still generally referred only to the polymer technologies most popular; the term AM was more generally used in metalworking contexts than among polymer/inkjet/Stereolithography enthusiasts. The term “Subtractive” has not replaced the term “machining,” instead complementing it when a terminology that covers any removal method is needed.
By the early 2010's, the terms “3D Printing” and “Additive Manufacturing” became overarching descriptors for all AM technologies. Although this was a departure from the earlier technically narrower nomenclatures, the generalization of the term reflects the simple fact that all the technologies employed to build objects share a commonality: The sequential layer-wise deposition of material, adjoining these successive layers throughout a 3D work envelope, under automated control.
Other vernacular terminologies have evolved, which are commonly used as AM synonyms, such as “Desktop Manufacturing (DM),” “Rapid Prototyping (RP),” also common vernacular, “Rapid Manufacturing (RM),” implying the industrial production-level successor to RP, and “On-Demand Manufacturing (ODM),” “Maker,” “Solid,” and other terms also joined the vocabulary set for the new art of 3D object creation.
The 2010's were the first decade in which metal parts such as engine brackets and large bolts and nuts would be built, (also referred to as “grown”), in job production, rather than having to be machined from bar stock or plate metal.
Current technological advances in 3D printing have grown to include the printing of biological materials, medical devices, dental implants and accessories, and even surgically implantable tissue-based materials.
General Principles
Understanding how the process works requires first that there be an object to print in a format that is translatable to mechanical replication. Thus, first the object to be printed has to be either scanned or created via three-dimensional rendering software. 3D printable models may be created with a computer aided design package, or via a 3D scanner, or via a plain, digital camera, and photogrammetry software. The manual modeling process of preparing geometric data for 3D computer graphics is similar to other plastic parts such as mold making and sculpting. 3D scanning is a process of analysis and collection of topographical, digital data of the surface shape and appearance of a real object. Based on this data, three-dimensional models of the scanned object can then be produced.
Regardless of the 3D modeling software used, the 3D model, (often in .skp, .dae, .3ds or some other format), then needs to be converted to either an .STL or an .OBJ format, to allow the printing software to be able to read it and deposit layers according to the desired build material, desired tolerances and other aspects.
With current technologies, before printing a 3D model from an STL file, the object file must first be examined for “manifold errors,” this step being called the “fixup.” .STL files that have been produced from a model obtained through 3D scanning are particularly vulnerable to many manifold errors that must be adjusted manually in the file before conversion of the file for printing. Examples of these manifold errors are surfaces that do not connect, or gaps in the models' surface.
Once adjusted, the .STL file needs to be processed by a software stage called a “slicer,” which converts the model into a series of thin layers. The layers are generated at the thickness appropriate for the predetermined build material and desired resolution. This produces a “G-code file” containing instructions tailored to a specific type of 3D printer. G-Code is a software language that sends discrete pulses to an electric motor, and thereby allows the user to control machine movement. In 3D printing, it instructs mechanical movement in the machine during the 3D printing process.
Printer resolution describes layer thickness and x/y resolution in dots-per-inch (DPI) or micrometers (μm). Typical layer thickness is around 100 μm (250 DPI)), although some machines can print layers as thin as 16 μm (1,600 DPI)). The x/y resolution is comparable to that of laser printers. The particles created are volumetric pixels, which has generated the term “Voxels,” (3D dots), and are generally around 50 to 100 μm, (510 to 250 DPI, or “Voxels Per Inch”—“VPI”), in diameter, the term “VPI” implying that the dimensions would be cubic.
Construction of an object with contemporary methods can take anywhere from several hours to several days, depending on the method used and the size and complexity of the model. This is a long period of time, even for the fastest methods, for the art to be adopted into serial ready-for-sale object manufacturing. Some additive systems can typically reduce this time to a few hours, although it varies widely, depending on the type of machine used and the size and number of models being produced simultaneously.
Errors often occur in the mechanical stage of the object building. These are caused by the print head, which moves along an x/y axis to at times inaccurately deposit material, or from the x, y, or z-axis, the vertical axis of the build surface, to be mechanically moved incorrectly to create mistakes in the object. This mechanical movement is problematic for many kinds of 3D printing.
Traditional techniques, such as injection molding can be less expensive for manufacturing polymer products in high volume quantities, but Additive Manufacturing can be faster, more flexible and less expensive when producing relatively small quantities of parts or custom parts. However, in general it is not fast enough to replace injection molding.
3D printers give designers and concept development teams the ability to produce parts and concept models, often using a desktop-sized printer or a convenient outside Service Bureau, wherein one may find several kinds of 3D printers, and one may choose the material and method suitable to one's needs, both material and budgetary. The cost of the printed prototype, cost and choice of materials, and color capabilities all are decision influencers.
The problem of distortion of built objects has been dealt with in several ways, for example, though the printer-produced resolution is sufficient for many applications, printing a slightly oversized version of the desired object in standard resolution and then removing material with a higher-resolution subtractive process can achieve greater precision, particularly because some distortion of the built object can occur when the materials are fully polymerized or temperature stabilized enough for final dimensional rendering.
Some printable polymers allow the surface finish to be smoothed and improved using chemical vapor processes.
Some additive manufacturing techniques are capable of using multiple materials in the course of constructing parts. These techniques are able to print in multiple colors and color combinations simultaneously, and would not necessarily require painting.
Some printing techniques require internal supports to be built for overhanging features during construction. These supports must be mechanically removed or dissolved upon completion of the build.
In metal printing, 3D printing allows substrate surface modifications to remove aluminum or steel.
Example Processes and Machines
Many different 3D printing processes have been invented since the late 1970's. The printers were originally large, expensive, and highly limited in what they could produce.
A large number of additive processes are now available. The main differences between processes are in the way layers are deposited to create parts, and in the materials that are used.
Some methods melt or soften material to produce the layers, e.g. selective laser melting (SLM) or direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM), or fused filament fabrication (FFF), while others cure liquid materials using different sophisticated technologies, e.g. Stereolithography (SLA). With laminated object manufacturing (LOM), thin layers are cut to shape and joined together (e.g. paper, polymer, metal). Each method has its own advantages and drawbacks.
Printers that work directly with metals are expensive. In some cases, however, less expensive printers can be used to make a mold, which is then used to make metal parts.
There are presently many existing types of three-dimensional prototyping machines that are controlled by computers. Usually a software-aided design platform sends commands to a machine in the form of subdivided two-dimensional frames of material deposition or subtraction, which involves stepper motor movements and/or material nozzle deposition done either by extrusion, jetting as in an inkjet type of precision droplets, or an actinic beam such as an ultraviolet or electron beam scanned mechanically over a sequentially stepped volume of uncatalyzed monomer. Powder sintering from additive layers is also a popular method wherein sequential layers of powder are sintered by jetted liquids or by heat from a scanning laser. Each of the present three dimensional prototyping types of machines have various advantages for various markets but they have inertial speed limitations due to the mechanical carriage assemblies which are involved in the material deposition or subtraction process. This new machine design, apparatus and method will be able to greatly and even exponentially surpass the present speeds of three dimensional prototyping machines, largely by eliminating the mechanical apparatus most responsible for taking the most time depositing or subtracting sequential layers of object material.
Key problems with conventional methods and designs include: slowness of build, mechanically complex machines, limited materials, limited material selection, weak or brittle materials, requirement for after-processing, distortion, lack of photorealistic color, cumbersome mechanical housings, complicated electronics, expensive, not user-friendly, and most significantly, not cost effective enough, fast enough, or accurate enough for industrial ready-for-sale manufacturing.
Examples of extrusion methods include and fused Deposition Modeling (FDM), Fused Filament Fabrication (FFF). These generally use thermoplastics, eutectic metals, edible materials, rubbers, modeling clay, metal clay (including precious metal clay), wherein filament or material is fed through a melting head, which then deposits molten plastic and it hardens as it cures.
Robocasting or Direct Ink Writing (DIW). These generally use ceramic materials, Metal alloy, cermet, metal-matrix composite, ceramic matrix composite.
Light Polymerized: Stereolithography (SLA) photopolymer, and Digital Light Processing (DLP) photopolymer.
Photopolymers are cured using a laser UV light source, which traces the object on the x/y place and the stacks layer in a z direction drop the previously cured layer.
Powder Bed includes the powder bed and inkjet head 3D printing (3DP). This can use almost any metal alloy, powdered polymers, and plaster, for example.
Electron-beam melting (EBM) can use almost any metal alloy including Titanium alloys.
Selective laser melting (SLM) can use titanium alloys, cobalt chrome alloys, stainless steel, and aluminum.
Selective Heat Sintering (SHS) can use thermoplastic powder.
Selective Laser Sintering (SLS) can use thermoplastics, metal powders, ceramic powders, photopolymers.
Direct metal laser sintering (DMLS) can use many metal alloys, but we must differentiate DMLS from EBM (electron beam melting), which requires a vacuum and avoids most severe oxidation effects. DMLS has many exceptions for metals because of oxidation problems.
Laminated includes laminated object manufacturing (LOM) using paper, metal foil, plastic film.
Electron Beam Freeform Fabrication (EBF3) can use almost any metal alloy
Extrusion Deposition
Fused deposition modeling (FDM) was developed by S. Scott Crump in the late 1980's and was commercialized in 1990 by Stratasys. After the patent on this technology expired, a large open-source development community developed and both commercial and DIY variants utilizing this type of 3D printer appeared. As a result, the price of this technology has dropped by two orders of magnitude since its creation.
In fused deposition modeling, the model or part is produced by extruding small beads of material, which harden immediately to form layers. A thermoplastic filament or metal wire that is wound on a coil is unreeled to supply material to an extrusion nozzle head, (3D printer extruder). The nozzle head heats the material and turns the flow on and off. Typically stepper motors or servo motors are employed to move the extrusion head and adjust the flow. The printer usually has three axes of motion (x/y/z). A computer-aided manufacturing (CAM) software package is used to generate the G-Code that is sent to a micro-controller, which controls the motors. Extrusion in 3D printing using material extrusion involves a cold end and a hot end.
Various polymers are used, including acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polylactic acid (PLA), high-density polyethylene (HDPE), PC/ABS, polyphenylsulfone (PPSU), and high impact polystyrene (HIPS). In general, the polymer is in the form of a filament fabricated from virgin resins. There are multiple projects in the open-sourced community aimed at processing post-consumer plastic waste into filament. These involve machines used to shred and extrude the plastic material into filament.
FDM is somewhat restricted in the variation of shapes that may be fabricated. For example, FDM usually cannot produce stalactite-like structures, since they would be unsupported during the build. Otherwise, a thin support must be designed into the structure, (a sprue), which can be broken away during finishing. Fused deposition modeling is also referred to as fused filament fabrication (FFF) by companies who do not hold the original patents as does Stratasys.
Binding of Granular Materials
Another 3D printing approach is the selective fusing of materials in a granular bed. The technique fuses parts of the layer and then moves downward in the working area, then adding another layer of granules and repeating the process until the piece has built up. This process uses the un-fused media to support overhangs and thin walls in the part being produced, which reduces the need for temporary auxiliary supports for the piece. A laser is typically used to sinter the media into a solid. Examples include selective laser sintering (SLS), with both metals and polymers (e.g. PA, PA-GF, Rigid GF, PEEK, PS, Alumide, Carbonmide, elastomers), and direct metal laser sintering (DMLS).
Selective Laser Sintering (SLS) was developed and patented by Dr. Carl Deckard and Dr. Joseph Beaman at the University of Texas at Austin in the mid-1980's, under sponsorship of DARPA. A similar process was patented without being commercialized by R. F. Householder in 1979.
Selective laser melting (SLM) does not use sintering for the fusion of powder granules, but will completely melt the powder using a high-energy laser to create fully dense materials in a layer-wise method that has mechanical properties similar to those of conventional manufactured metals.
Electron beam melting (EBM) is a similar type of additive manufacturing technology for metal parts (e.g. titanium alloys). EBM manufactures parts by melting metal powder layer by layer with an electron beam in a high vacuum. Unlike metal sintering techniques that operate below melting point, EBM parts are fully dense, void-free, and very strong
Another method consists of an inkjet 3D printing system. The printer creates the model one layer at a time by spreading a layer of powder (plaster, or resins) and printing a binder in the cross-section of the part using an inkjet-like process. This is repeated until every layer has been printed. This technology allows the printing of full color prototypes, overhangs, and elastomer parts. The strength of bonded powder prints can be enhanced with wax or thermoset polymer impregnation.
Laminated Object Manufacturing
In some printers, paper can be used as the build material, resulting in a lower cost to print. During the 1990's, some companies marketed 3D printers that cut cross sections out of special adhesive-coated paper using a carbon dioxide laser, and then laminated them together.
In 2005 Mcor Technologies Ltd. developed a different process using ordinary sheets of office paper, a tungsten carbide blade to cut the shape, and selective deposition of adhesive and pressure to bond the prototype.
There are also a number of companies selling printers that print laminated objects using thin plastic and metal sheets.
Stereolithography
Stereolithography was patented in 1986 by Charles Hull. Photopolymerization is primarily used in Stereolithography (SLA) to produce a solid part from a liquid. SLA uses a laser beam to selectively cure photosensitive liquid into the desired form in sequential x/y layers. Stereolithography (SL) is widely recognized as the first 3D printing process and first to be commercialized. SL is a laser-based process that works with photopolymer resins that react with the laser and cure to form a solid in a very precise way to produce very accurate parts. It is a complex process, but simply put, the photopolymer resin is held in a vat with a movable platform inside. A laser beam is directed in the x/y axes across the surface of the resin according to the 3D data supplied to the machine (the .stl file), whereby the resin hardens precisely where the laser hits the surface. Once the layer is completed, the platform within the vat drops down by a fraction (in the z axis) and the subsequent layer is traced out by the laser. This continues until the entire object is completed and the platform can be raised out of the vat for removal.
Because of the nature of the SL process, it requires support structures for some parts, specifically those with overhangs or undercuts. These structures need to be manually removed.
In terms of other post processing steps, many objects 3D printed using SL need to be cleaned and cured. Curing involves subjecting the part to intense light in an oven-like machine to fully harden the resin.
Stereolithography is generally accepted as being one of the most accurate 3D printing processes with excellent surface finish. However limiting factors include the post-processing steps required and the stability of the materials over time, which can become more brittle.
Solid Ground Curing (SCG), also known as the Solider Process, is a process that was invented and developed by Cubital Inc. of Israel. The SGC process uses photosensitive resin hardened in layers as with the SLA process. However, in contrast to SLA, the SGC process is considered a high-throughput production process. The high throughput is achieved by hardening each layer of photosensitive resin at once rather than tracing it one row at a time. Many parts can be created at once because of the large workspace and the fact that a milling step maintains vertical accuracy. Wax replaces liquid resin in non-part areas with each layer so that model support is ensured.
These processes were a dramatic departure from the “photosculpture” method of Francois Willème (1830-1905), developed in 1860. The “photosculpture” method consisted of photographing a subject from a variety of equidistant angles and projecting each photograph onto a screen, where a pantograph was used to trace the outline onto modeling clay.
DLP—or digital light processing—is a similar process to stereolithography in that it is a 3D printing process that works with photopolymers. The major difference is the light source. DLP uses a more conventional light source, such as an arc lamp, with a liquid crystal display panel or a deformable mirror device (DMD), which is applied to the entire surface of the vat of photopolymer resin in a single pass, generally making it faster than SL. Also like SL, DLP produces highly accurate parts with excellent resolution, but its similarities also include the same requirements for support structures and post-curing. However, one advantage of DLP over SL is that only a shallow vat of resin is required to facilitate the process, which generally results in less waste and lower running costs. The EnvisionTEC Perfactory is an example of a DLP rapid prototyping system.
Inkjet printer systems like the Objet PolyJet system spray photopolymer materials onto a build tray in ultra-thin layers, (between 16 and 30 μm), until the part is completed. Each photopolymer layer is cured with UV light after it is jetted, producing fully cured models that can be handled and used immediately, without post-curing. The gel-like support material, which is designed to support complicated geometries, is removed by hand and water jetting. It is also suitable for elastomers. Ink jet printing of objects has become more rapid with the use of multiple heads or Multi-Jet Printing (MJP).
Ultra-small features can be made with the 3D micro-fabrication technique used in multi-photon-photo-polymerization. This approach uses a focused laser to trace the desired 3D object into a block of gel. Due to the nonlinear nature of photo excitation, the gel is cured to a solid only in the places where the laser was focused while the remaining gel is then washed away. Feature sizes of under 100 nm are easily produced, as well as complex structures with moving and interlocked parts.
Yet another approach uses a synthetic resin that is solidified using LEDs. In Mask-image-projection-based stereolithography a 3D digital model is sliced by a set of horizontal planes. Each slice is converted into a two-dimensional mask image. The mask image is then projected onto a photocurable liquid resin surface and light is projected onto the resin to cure it in the shape of the layer. The technique has been used to create objects composed of multiple materials that cure at different rates. In research systems, the light is projected from below, allowing the resin to be quickly spread into uniform thin layers, reducing production time from hours to minutes. Commercially available devices such as Objet Connex apply the resin via small nozzles.